During the Second World War there were severe food shortages in Britain.
Eggs were rationed, and for much of the time only imported powdered egg was available.
After the war there was a huge drive to increase domestic food production, and chickens were seen as a big part of the answer.
In the 1940s, chickens were a common sight in the British countryside.
They were mostly kept for eggs and would only be killed for meat when their egg-laying days were over.
Chicken was neither a common or particularly cheap meat.
Until the 1950s, rabbit was more popular on British dinner tables.
But in 1953 a British farmer managed to introduce a new hybrid chicken from America into the UK.
It was specially bred for a new way of rearing chickens; the factory farms.
On these farms there were two types of chicken, one for eating, and one for laying eggs.
And today no chicken we eat has ever laid an egg.
There was a revolution in the British diet.
In 1950 British consumers only ate one million chickens a year.
By the 60s it was a different story.
200 million chickens get eaten every year in Britain.
A further 60 million spend their lives laying eggs, enough for each of us to have an egg a day, every day of the year.
Chicken became central to the British diet.
The new intensive farms became the main method of rearing chickens.
Humans have shaped and　changed chickens enormously.
We've changed how quickly they grow and how frequently they lay eggs.

We first domesticated chickens 8,000 years ago.
In addition to them being easy to keep, they were also pretty easy to breed.
I've been to poultry shows up and down the country, and at every one you can see an astounding array of chickens.
In fact there are more than 200 different breeds of domestic chicken.
Every one of them effectively created by us.
Some, like the Leghorns, have been bred for egg laying.
Light Sussex chickens are dual purpose birds; good for eggs and meat.
Old English Game birds were originally kept for fighting.
And some, like the Frizzle, have just been bred for show.
With such a huge variety of chickens, of all different shapes and sizes, I do wonder where this species
came from in the first place.
Now you might be as surprised as I was to discover that there's a man at Oxford University who has spent the last ten years studying the chicken's wild ancestor.
I hope Dr Tom Pizzari can tell me a bit more about them.
I thought I'd show you what wild chickens actually look like.
There are wild chickens in South East Asia, they're called red jungle fowl.
And this is really the ancestral population that produced all the different breeds of domestic chicken.
Isn't it funny?
People, don't think of chickens being a wild animal.
No, absolutely not.
And yet, look, he's displaying exactly the same behaviour as the cockerels in the paddock.
Yeah, look at that.
Now looking at this wild bird here, this is a tropical bird living on a forest floor.
Why on earth did we domesticate this animal, the jungle fowl, rather than any other species of bird?
They're very social.
This means that people can keep them in large groups, which obviously helps.
They are highly adaptable, they have a very diverse diet, and they are able to live in a very wide range of
environments, from tropical forests to the foothills of the Himalaya.
Through to caged, commercial systems.
Absolutely, yes, they are a victim of their own success, in a way.
As animals, they're good all rounders?
They are.
They can be in the snow, they could be in hot climates, they like a varied diet.
Do you think one of the great reasons that they're domesticated is because they're pretty good to eat?
That's the third reason, absolutely, yes.
It's bad news if you're delicious, in other words.
Yes, absolutely, yes.
Chickens originated in Thailand but were brought to Europe 2,000 years ago.
From the 15th century, chickens were carried all over the world by European colonists.
We domesticated chickens for their eggs, their meat and even because we liked to see them fight.

Despite its appearance that cassowary is a relatively recent bird.
It is believed that it only separated from its primitive ancestor around 10,000 years ago.
On the other hand the other more normal-looking birds are among the oldest inhabitants of these Australian jungles.
The mound builders; a group of birds which were the first to become separated from the main branch of ornithological evolution.
The australian brush turkey is the most representative example of the australian mound builders.
The males build nests which can be up to a meter high by collecting to gether up to 4 tons of vegetable material.(あってるかぜんぜんわからん)
Tiny fungi live among the dead leaves decomposing them and releasing heat as they breathe.
In this way, the nest becomes a gigantic incubator.
In it a number of females lay their eggs and the male will look after them making sure that the temperature of the nest remains constant.
It is believed that somewhere on their tongues or beaks, the brush turkeys must have areas which are extremely sensitive to heat, and so during incubation, they plunge their heads down into the leaves and check that the temperature remains between 30 and 35 degrees centigrade.
This system which we might think is a recent original innovation is in fact the demonstration accepted by many scientists as proof of just how closely the mound builders are in evolutionary terms to the reptiles.
For only reptiles and the group of brush turkeys use this particular and effective system of incubation.

Just as ibex attain sanctuary on the cliffs, so all animals gain protection from the monasteries.
To Buddhists, all life is linked in an endless cycle of death and rebirth.
Every turn of the wheel releases the power of prayer.
With this belief comes respect for all living things, so the surroundings of the monasteries are often a haven for wildlife.
Safe from human persecution, chukor partridge shelter below the walls of the monastery.
From the monasteries, the word reaches far into the mountains.

In peafowl society there's no such thing as an easy hookup.
Nothing happens without elaborate ritual and fanfare.
Peacocks are the most shallow of all male birds.
I mean, they go through this whole thing.
They turn their back to the female, then rustle their little white fluffy tail feathers.
And then, they flip around and dazzle.
What that looks like to a female peahen I can only imagine because birds have much more brilliant color vision than we do.
They have much more refined color vision.
The male carries all the weight in these encounters.
It is he who has to impress because his chances are only as good as his tail.
It's the male peacock who has the long showy tail but it's really female choosiness that's driven the
evolution of that tail.
Peafowl think the more impressive the tale the better the genes they'll pass on to their young.
Competition among males is fierce as they go tail to tail in a display called a lek.
It's sort of like an animal nightclub.
In other words, the males sing and dance and the females wander around and decide who they want to have sex with.
These male beauty pageants are make or break for auditioning wannabe fathers.
Because, in the bizarre world of animal courtship, the stakes are high.
If a female peahen remains unimpressed, the male's out of luck.
No sex, no offspring, no genes passed on.
Often its females who hold the whip hand in the animal kingdom.
So what does a desperate male do?
He resorts to the dirty tricks department.

Something appears out of the brush.
Survivors of the glacial period, ptarmigans are the only birds in Japan surviving year-round in this Alpine
environment.
The bountiful fruits found in autumn provide a veritable feast for these creatures.
It's favorite bog blueberries.
Once full he moves off to find another spot.
In the afternoon the rising warm air is suddenly cooled as it reaches the mountaintop.
This forms into mist.
The ridge is engulfed in a moment.
Ptarmigan chicks emerge from the cover of the pines.
Only three months old, they are already as big as their parents.
The mist conceals the chicks from predators such as Eagles, giving them a chance to look for food.
One of the chicks ventures out.
The others soon follow.
Feeding on cranberries as their mother watches over.
All the mountain creatures are now preparing for winter.